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Re: Dave's autoformer

Hello, Jim.
How did you guess that I have a stash of 26 ?
I actually tried Dave's autoformer before a Berman 6SN7 line stage and battery-run 7308 line stage of my own design. In both cases, the tubes added hiss and did not add the usual tube smoothness. What I heard was congestion and dynamic restriction, compared to the pure autoformer.
With the autoformers, the sound quality I get at home is at the same time smooth, liquid and very transparent; musical but also very fast and dynamic. Those are usually mutually exclusive qualities when you design around a resistive attenuator.
I guess that tube's predominant second harmonic distortion kinda offsets the leanness of most metal film attenuators.

With an R attenuator, usually I get muffled, undynamic sound below 9 o'clock on the dial, it sounds OK and balanced around twelve o'clock and too transparent/metallic close to the max volume.
By attenuator, I mean Dact, Goldpoint, Alps and TKD stepped resistive attenuators. Noble and carbon pots sound slightly inferior, they gloss over the details.
If your primary source is CD or a high output phono stage, there is really no need for gain in a line stage. Dave's autoformers pass from DC to 100Khz (my guesstimate) and add no noise or distortion that I can hear.
They do not sound euphonic, however, their sound is so clean and pure that it gets addictive after a while.
BTW I love tubes. Probably the ideal amplifier (for me) would be an integrated 20W tube amp with autoformers as volume controls: one less component, one less interconnect, shorter signal path.
I hope this helps, but I am certain you forgot more about tubes than I ever expect to learn. :^)
Carlos



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